A V-belt continuously variable transmission and a toroidal continuously variable transmission for a vehicle are generally controlled so that a real drive ratio of the transmission follows a target drive ratio calculated from the throttle opening of the engine and the vehicle speed.
As a result, when a driver depresses an accelerator pedal to accelerate the vehicle, the target drive ratio increases, that is, varies toward the low speed side, and the transmission performs a shift-down.
When the driver returns the accelerator pedal, the target drive ratio decreases, i.e. varies toward the high speed side, and the transmission performs a shift-up.
Tokkai Hei 7-172217 published in 1995 by the Japanese Patent Office discloses a vehicle with an automatic transmission in which the engine output and the drive ratio are controlled so that the vehicle drive force coincides with a target value.
The engine and transmission are controlled in such a way that when the accelerator pedal is depressed by a small amount, continuity of drive force is emphasized, and when the accelerator pedal is depressed by a large amount, obtaining a large drive force is emphasized.
However, this prior art is not necessarily effective in economizing the fuel consumption of the engine.
Further, the prior art has the premise that the transmission is a planetary gear type automatic transmission wherein the drive ratio varies in a stepwise manner. In the aforesaid continuously variable transmission, however, the drive ratio varies continuously by nature, so specific control to maintain the continuity of drive force is not necessary.